Undersea Weapons

Probably the most effective of all methods of attack in naval warfare is the use of weapons such as the torpedo, the mine and the depth charge, which are particularly dangerous because they strike below the water-line

THE NAVY GOES TO WORK - 11

DEPTH CHARGES on the deck of HM flotilla leader Kempenfelt. Specially designed for use against submarines, the modern depth charge is a metal cylinder 20 in long and 18 in in diameter. It contains 300 lb of TNT (trinitrotoluene) and will disable a submarine that is caught within 70 feet of the explosion. The Kempenfelt, built in 1933, has a displacement of 1,390 tons, and her geared turbines of 36,000 horse-power give her a speed of over 35 knots. In the background is the destroyer Viceroy, 1,120 tons displacement.

THE fact that every combatant ship in the Royal Navy, other than the sloop, is armed with torpedoes is striking evidence of the respect in which this weapon is held. Compared with the gun the torpedo is not, and is never likely to be, an arm of precision. It has been aptly described as “a weapon of opportunity”, in the use of which chance must always play a big part. But when the torpedo does strike home the effect of its blow is, as a rule, far more deadly than that of the heaviest gun projectile. This is because the blow is delivered well below the waterline, rupturing the hull of the ship and admitting the sea.

Unless, therefore, a torpedoed ship is efficiently sub-divided into watertight compartments she is in grave danger of sinking. It is mainly due to the influence of the torpedo that every modern man-of-war is honeycombed with these compartments. Many battleships and cruisers have, in addition, an external “bulge”, or false hull, to absorb the shock of an underwater explosion and prevent it from blowing in the hull proper.

The first locomotive torpedo was produced about seventy years ago by the joint efforts of an Austrian naval officer, Captain Luppis, and a British engineer, Robert Whitehead. Having, studied the effects of underwater attack in the American Civil War, during which many vessels were destroyed in this way, Luppis cast about for a method by which an explosive mine could be self-propelled towards the ship, instead of having to wait until the ship ran into it.

The original locomotive torpedo was a cigar-shaped iron case, propelled by compressed air working a small engine and screw in the tail of the “fish”. Whitehead realized that as the air escaped the torpedo would continually become lighter, until, towards the end of its run, it would rise to the surface. To overcome this tendency he invented a mechanism which used

the pressures due to varying depths of water to operate horizontal rudders.

Thus, when the torpedo tries to rise above the horizontal plane at which it is set to run, the rudders automatically force it back to the proper depth. Conversely, if for any reason the torpedo tends to dive below that depth, it is brought back to the true plane by the reflex action of the rudders.

Whitehead’s first torpedo carried in the nose a charge of gunpowder detonated by percussion. When demonstrated before naval experts the new weapon proved a great success, and the Whitehead torpedo was immediately adopted by all important navies. Its principal defect was low speed — only 8 knots — but this was soon remedied by the introduction of the famous Brotherhood three-cylinder air engine, which raised the velocity to 18 knots. At the same time guncotton superseded ordinary gunpowder as a “war head”, and as the gun-cotton was a much more powerful explosive it was possible to use a smaller torpedo. As adopted by the Royal Navy in the 1870s the Whitehead torpedo was 11 feet long, with a diameter of 11 in., the total weight being just over 5 cwt. The nose of the missile was fined down to a sharp point, but later experiments with submerged bodies showed that a bulbous or bluff head offered less resistance to the water and therefore gave greater speed. Further, the new form of head enabled the explosive charge to be increased without lengthening the torpedo itself. Speed was gradually increased until, by 1895, the torpedo could travel at 27 knots for a distance of 600 yards.

Since those far-off days the torpedo has advanced in efficiency by gradual stages but without any modification of its fundamental features. The diameter has increased to 21 in., improved engines and a system of pre-heating the compressed air have raised the speed to 50 knots and the maximum range to 15,000 yards, while the explosive charge has grown to 550 lb. of T.N.T. (trinitrotoluene).

The largest torpedo of which the existence has been publicly disclosed is the British 24½-in. model, used exclusively in the battleships Nelson and Rodney. Apart from these monster “fish” the standard British torpedo is the 21-in., of which no official details are available. The following particulars of the modern Italian torpedo, which is probably typical, have been published: diameter 21 in., length 23¼ feet, weight 2 tons, explosive charge 550 lb., speeds — at 4,000 yards, 50 knots; at 6,000 yards, 43 knots; at 8,000 yards, 39 knots; at 10,000 yards 34 knots; at 12,000 yards, 30 knots. Smaller types of torpedo have been developed for the use of aircraft.

FIRING A TORPEDO from H.M.S. Cornwall. Modern torpedoes have a diameter of about 21 in. and are charged with about 550 lb. of T.N.T. The monster “ fish” enters the water at a speed of about 50 knots. H.M.S. Cornwall is a cruiser of the Kent class, built in 1928, and has a displacement of 9,750 tons.

The usual method of discharging the torpedo is from a tube of corresponding diameter. The torpedo fits snugly in the tube, along the upper part of which there is a groove engaging a lever fixed to the torpedo. Discharge is effected either by powder or compressed air, and as the torpedo shoots forward the lever is tripped by a catch in the tube and the engines are set in motion. Thus, before the torpedo enters the water its twin propellers are revolving at high speed. The torpedo is first set to run for a certain distance and at a given depth, and once the necessary adjustments have been made the control mechanism does the rest.

Menace to Friend and Foe

In peace-time practice a soft-metal head filled with water is substituted for the explosive war head, so that when the target is hit the head collapses and the torpedo, itself undamaged, rises to the surface and is picked up. Recovery is aided by the burning of a calcium flare which automatically ignites when the torpedo breaks surface. In war a special device is fitted which causes the torpedo to sink at the end of its run, for if left floating on the surface it would be a menace to friend no less than to foe.

Destroyers, as well as all modern cruisers, carry deck torpedo tubes which can be trained through a wide arc on either beam. In most battleships, however, the tubes are submerged and fixed, and the ship herself must be manoeuvred to bring the torpedo sights to bear on the target. To fire a torpedo from a submerged tube when the ship is steaming at high speed is not a simple operation. Were the torpedo just shot out of the tube the rush of water along the side would be liable to damage the weapon. To avoid this a steel screen, or “spoon”, of the same length as the torpedo, is thrust out from the side of the ship, parallel with the tube, just before firing. The torpedo is then discharged, and being protected by the “spoon”, it has time to attain speed before meeting the rush of water.

Thanks to the development of torpedo sighting and director appliances, excellent practice is now made even at long range, though war experience proved that with torpedoes fired from surface ships the proportion of hits is low. A submarine has the advantage of being able to approach the target more closely and, as a rule, its presence is not detected up to the moment of firing. For these reasons the percentage of hits made by torpedoes fired from submarines is comparatively high. It would undoubtedly be much higher but for the difficulties inherent in aiming through a periscope.

Two factors which, either separately or jointly, have enabled many a vessel to evade torpedo attack are the upheaval of water caused by discharge from a submerged position and the tell-tale track of air bubbles left by the torpedo itself. Naval inventors are working hard to eliminate these factors, and apparently with success. In the first place devices have been evolved for rendering torpedo discharge invisible, while the introduction of electrically-driven torpedoes, already under experiment, may eventually overcome the second drawback.

The naval mine is a weapon of some antiquity. It took a heavy toll of ships in the American Civil War, and forty years later proved an almost decisive instrument in the Russo-Japanese struggle. During the war of 1914-18 it caused more casualties at sea than any arm, excepting the torpedo. According to official statistics nearly 250,000 mines were laid by the various belligerents, including 112,354 by British ships in the North Sea alone.

The modern naval mine is a pear-shaped buoy about 3 feet in diameter, with a total weight of 650 lb. when loaded. It is charged with 350 lb. of high explosive, usually T.N.T. (trinitrotoluene), which occupies half the available space, the other half being used as an air chamber to keep the mine buoyant. From the top of the iron casing project half a dozen “horns” of lead each enclosing a glass tube filled with a chemical mixture. When one of these horns is struck by a ship or other heavy object the glass tube is fractured, and the chemical liquid pours down on to a battery which promptly detonates the charge. As the mine is submerged several feet below the surface the whole force of the explosion is directed upwards, with dire results to the object which has fouled the mine.

Mines may be laid at almost any depth. They are kept at the required distance from the surface by heavy sinkers, to which they are attached by steel cables. Minelaying can be, and has been, performed by every class of vessel, from battleship to submarine.

Efficiency of Paravanes

Unlike the torpedo, the mine gives no warning of its presence unless it becomes detached from its cable by chafing or heavy weather and bobs up to the surface, where it is still a menace unless detected in time.

On the other hand, the explosion of a single mine may reveal the existence of a whole field, as so often happened in 1914-18. Then the minesweepers are brought into play. Two trawlers or other light-draught vessels, towing between them a sweep wire, steam over the suspected area, and if they are fortunate fish up all the mines in their path. This is the original method of minesweeping and it is still in vogue, though it has been supplemented and may in the end be superseded by the paravane.

This device is an adaptation of the fisherman’s “otter”. In shape it resembles a squat torpedo equipped with fixed fins and a rudder actuated by water pressure. It is also fitted with a pair of steel jaws resembling the teeth of a shark. Two paravanes are carried by a ship, to the forefoot of which they are attached by wire cables. As the vessel forges ahead the action of the fins causes the paravane to stream away from the bows at an angle of 50 degrees, while the rudder keeps it at a fixed depth below the surface. Thus the vessel is protected by a V-shaped barrier of taut steel wire. When a submerged mine is encountered its mooring cable is caught by the paravane wire and deflected into the steel jaws of the paravane, which instantly sever it. The released mine then bobs up to the surface, well away from the ship, and is easily disposed of by gunfire.

Various forms of paravane have been evolved to suit different ships, including a special type which can be towed astern at high speed by destroyers. As far as is known, no ship equipped with paravanes was ever damaged by a mine during the war of 1914-18. The device is therefore of considerable protective value, though it would be going too far to assert that it has entirely overcome the mine peril.

Last, but not least, among the Navy’s undersea weapons is the depth charge, a type of mine specially designed for anti-submarine purposes. It consists of a metal cylinder 28 in. long with a diameter of 18 in. containing 300 lb. of T.N.T. It is fitted with a hydrostatic firing valve which can be adjusted to explode the charge at almost any depth of water. When the presence of a hostile submarine is detected or suspected, the nearest destroyers release their depth charges, and a few seconds later the sea is convulsed with terrific explosions far below the surface. It is estimated that a heavy depth charge will disable a submarine if it detonates within a radius of 70 feet.

STRUCK BY A TORPEDO “END-ON” the stem of the Harrison liner Explorer was almost completely destroyed. The division of the modern steamship into watertight compartments has done much to prevent her sinking when the hull is pierced below the water-line.

You can read more on “Big Guns in Action”, “Design of the Torpedo”, and “The Ship and the Gun” on this website.